HSP90s are ubiquitous chaperone proteins that are involved in folding, activation and assembly of a wide range of proteins, including key proteins involved in signal transduction, cell cycle control and transcriptional regulation. Researchers have reported that HSP90 chaperone proteins are associated with important signaling proteins, such as steroid hormone receptors and protein kinases, including, e.g., Raf-1, EGFR, v-Src family kinases, Cdk4, and ErbB-2 (Buchner J. TIBS 1999, 24, 136–141; Stepanova, L. et al. Genes Dev. 1996, 10, 1491–502; Dai, K. et al. J. Biol. Chem. 1996, 271, 22030–4). Studies further indicate that certain co-chaperones, e.g., HSP70, p60/Hop/Sti1, Hip, Bag1, HSP40/Hdj2/Hsj1, immunophilins, p23, and p50, may assist HSP90 in its function (see, e.g., Caplan, A. Trends in Cell Biol. 1999, 9, 262–68).
Ansamycin antibiotics, e.g, herbimycin A (HA), geldanamycin (GM), and 17-allylaminogeldanamycin (17-AAG) are thought to exert their anticancerous effects by tight binding of the N-terminus pocket of HSP90, thereby destabilizing substrates that normally interact with HSP90 (Stebbins, C. et al. Cell 1997, 89, 239–250). This pocket is highly conserved and has weak homology to the ATP-binding site of DNA gyrase (Stebbins, C. et al., supra; Grenert, J. P. et al. J. Biol. Chem. 1997, 272, 23843–50). Further, ATP and ADP have both been shown to bind this pocket with low affinity and to have weak ATPase activity (Proromou, C. et al. Cell 1997, 90, 65–75; Panaretou, B. et al. EMBO J. 1998, 17, 4829–36). In vitro and in vivo studies have demonstrated that occupancy of this N-terminal pocket by ansamycins and other HSP90 inhibitors alters HSP90 function and inhibits protein folding. At high concentrations, ansamycins and other HSP90 inhibitors have been shown to prevent binding of protein substrates to HSP90 (Scheibel, T. H. et al. Proc. Natl. Acad. Sci. USA 1999, 96, 1297–302; Schulte, T. W. et al. J. Biol. Chem. 1995, 270, 24585–8; Whitesell, L., et al. Proc. Natl. Acad. Sci. USA 1994, 91, 8324–8328). Ansamycins have also been demonstrated to inhibit the ATP-dependent release of chaperone-associated protein substrates (Schneider, C. L. et al. Proc. Natl. Acad. Sci., USA 1996, 93, 14536–41; Sepp-Lorenzino et al. J. Biol. Chem. 1995, 270, 16580–16587). In either event, the substrates are degraded by a ubiquitin-dependent process in the proteasome (Schneider, C. L., supra; Sepp-Lorenzino, L., et al. J. Biol. Chem. 1995, 270, 16580–16587; Whitesell, L. et al. Proc. Natl. Acad. Sci. USA 1994, 91, 8324–8328).
HSP90 substrate destabilization occurs in tumor and non-transformed cells alike and has been shown to be especially effective on a subset of signaling regulators, e.g., Raf (Schulte, T. W. et al. Biochem. Biophys. Res. Commun. 1997, 239, 655–9; Schulte, T. W., et al. J. Biol. Chem. 1995, 270, 24585–8), nuclear steroid receptors (Segnitz, B.; U. Gehring J. Biol. Chem. 1997, 272, 18694–18701; Smith, D. F. et al. Mol. Cell. Biol. 1995, 15, 6804–12), v-Src (Whitesell, L., et al. Proc. Natl. Acad Sci. USA 1994, 91, 8324–8328) and certain transmembrane tyrosine kinases (Sepp-Lorenzino, L. et al. J. Biol. Chem. 1995, 270, 16580–16587) such as EGF receptor (EGFR) and HER2/Neu (Hartmann, F., et al. Int. J. Cancer 1997, 70, 221–9; Miller, P. et al. Cancer Res. 1994, 54, 2724–2730; Mimnaugh, E. G., et al. J. Biol. Chem. 1996, 271, 22796–801; Schnur, R. et al. J. Med Chem. 1995, 38, 3806–3812), CDK4, and mutant p53. Erlichman et al. Proc. AACR 2001, 42, abstract 4474. The ansamycin-induced loss of these proteins leads to the selective disruption of certain regulatory pathways and results in growth arrest at specific phases of the cell cycle (Muise-Heimericks, R. C. et al. J. Biol. Chem. 1998, 273, 29864–72), and apoptosis, and/or differentiation of cells so treated (Vasilevskaya, A. et al. Cancer Res., 1999, 59, 3935–40). Ansamycins thus hold great promise for the treatment and/or prevention of many types of cancers and proliferative disorders, and also hold promise as traditional antibiotics. However, their relative insolubility makes them difficult to formulate and administer, and they are not easily synthesized and currently must, at least in part, be generated through fermentation. Further, the dose limiting toxicity of ansamycins is hepatic.
In addition to anti-cancer and antitumorgenic activity, HSP90 inhibitors have also been implicated in a wide variety of other utilities, including use as anti-inflammation agents, anti-infectious disease agents, agents for treating autoimmunity, agents for treating stroke, ischemia, multiple sclerosis, cardiac disorders, central nervous system related disorders and agents useful in promoting nerve regeneration (See, e.g., Rosen et al. WO 02/09696 (PCT/US01/23640); Degranco et al. WO 99/51223 (PCT/US99/07242); Gold, U.S. Pat. No. 6,210,974 BI; DeFranco et al., U.S. Pat. No. 6,174,875. Overlapping somewhat with the above, there are reports in the literature that fibrogenetic disorders including but not limited to scleroderma, polymyositis, systemic lupus, rheumatoid arthritis, liver cirrhosis, keloid formation, interstitial nephritis, and pulmonary fibrosis also may be treatable with HSP90 inhibitors. Strehlow, WO 02/02123 (PCT/US01/20578). Still further HSP90 modulation, modulators and uses thereof are reported in Application Nos. PCT/US03/04283, PCT/US02/35938, PCT/US02/16287, PCT/US02/06518, PCT/US98/09805, PCT/US00/09512, PCT/US01/09512, PCT/US01/23640, PCT/US01/46303, PCT/US01/46304, PCT/US02/06518, PCT/US02/29715, PCT/US02/35069, PCT/US02/35938, PCT/US02/39993, 60/293,246, 60/371,668, 60/335,391, 60/128,593, 60/337,919, 60/340,762, 60/359,484 and 60/331,893.
Recently, purine derivatives showing HSP90 inhibitory activity have been reported, e.g., in PCT/US02/35069 and PCT/US02/36075. Purine moieties are well accepted bioisosteres for a variety of ATP-dependent molecular targets, see, JP 10025294; U.S. Pat. No. 4,748,177; U.S. Pat. No. 4,772,606; U.S. Pat. No. 6,369,092; WO 00/06573; WO 02/055521; WO 02/055082; WO 02/055083; EP 0178178; Eur. J. Med. Chem. 1994, 29(1), 3–9; and J. Het. Chem. 1990, 27(5), 1409. However, compounds having the desired potency, selectivity and pharmaceutical properties required for effective HSP90 inhibition in vivo have not been reported. Therefore, a need remains for additional novel and potent HSP90 inhibitors that meet the demanding biological and pharmaceutical criteria required to proceed towards human clinical trials.